Stabilized photographic material with tetrazole thiocarbonic acid ester

ABSTRACT

This invention relates to a photographic silver halide emulsion the stability of which is improved by addition of substituted 5mercapto-tetrazole derivatives.

United States Patent Wolfgang Muller-Bardorff Cologne;

Wilhelm Saleck, Schildgen, Bergisch- Gladbach; Franz Moll, Cologne,Stammheim, all of Germany [21] App]. No. 780,885

[72] Inventors [54] STABILIZED PHOTOGRAPI-IIC MATERIAL WITH TETRAZOLETI-IIOCARBONIC ACID ESTER 5 Claims, No Drawings [52] US. Cl 96/109,

[51] Int. Cl G03c 1/34 [50] Field of Search 96/665, 109

[56] References Cited UNITED STATES PATENTS 3,071,465 l/l963 Dersch etal 96/109 X 3,244,521 4/1966 Dersch et al.... 96/109 X 3,311,474 3/1967Willems etal. 96/109X Primary ExaminerNorman G. Torchin AssistantExaminer-John L. Goodrow Attorney-Connolly and I-Iutz ABSTRACT: Thisinvention relates to a photographic silver halide emulsion the stabilityof which is improved by addition of substituted S-mercapto-tetrazolederivatives.

STABILIZED PHOTOGRAPHIC MATERIAL WITH TETRAZOLE TI-IIOCARBONIC ACIDESTER It is well known that photographic emulsions on storage becomespontaneously developable without exposure to light. There is normally adetectable amount of the silver salt reduced during development atunexposed areas. This phenomenon is commonly called fog or chemical fog.Fog depends both upon the nature of the emulsion and the conditions ofdevelopment. For a given emulsion it increases with the degree ofdevelopment. It is common practice to make accelerated tests of thestability of photographic emulsions by storage at increased temperatureor humidity, or both. It is desirable to have emulsions as stable aspossible under the condition of high temperature, which may occur intropical climates. Fog usually appears over the whole area of thelightsensitive layer, but when severe is quite frequently nonuniform.

It is known that certain compounds particularly heterocyclic mercapto orimino compounds have an antifoggant and stabilizing effect whenincorporated into photographic silver halide emulsions and so improvegreatly the keeping qualities of the emulsions. Mostly theso-calledfog-inhibitors or stabilizers'form difficultly soluble orinsoluble silver compounds with the silver ions of the photographicemulsion. It is also known that inorganic or organic mercury compoundscan be used. Many of these stabilizers however, are of limited utilitysince they have a desensitizing effect or alter the gradation.

It is among the objects of the invention to provide stabilizers whichcause no reduction in the sensitivity at concentrations at which theyachieve sufficient stabilization. Another object is torprovide aphotographic silver halide emulsion that is stable against theproduction of fog upon storage and stable with respect to the speed andcontrast of the emulsion. Other objects and advantages will becomeapparent from a consideration of the following description and examples.

We now have found that photographic silver halide emulsions can bestabilized with respect to the formation of fog even under extremestorage conditions and with respect to speed and contrast of theemulsion very effectively by the addition of S-mercaptotetrazolederivatives of the following formula:

in which:

Rl is a hydrocarbon radical, in particular alkyl, preferably containingone to three carbon atoms, such as ethyl or propyl, or aryl, inparticular a radical of the phenyl series, or aralkyl such as benzyl orphenyl ethyl;

Y represents (1 the grouping which is' linked to the carbonyl groupthrough an oxygen or sulfur atom or (2) the group NR2R3 and R stands foralkyl having preferably up to five carbon atoms or for a radical of thephenyl series such as phenyl which may be substituted, for example, withhalogen such as chlorine or bromine, alkyl having up to five carbonatoms such as methyl or ethyl, alkoxy or alkylthio, the alkyl groupsofwhich having up to five carbons atoms. R stands for hydrogen or for RParticular utility is exhibited by the following compounds:

The compounds can be made by reacting l-substituted mercaptotetrazolesknown per se, for example in the form of their alkali metal salts, withan excess of phosgene to convert them into the chlorocarbonic acidthioesters. Further reaction with amines produce compounds such as 5-8,and with alkali metal salts of a mercaptotetrazole compound yieldcompounds such as l-4. It is also possible to react theS-mercaptotetrazoles with isocyanates, thereby obtaining compounds suchas 5, 6, or 7. The alkali metal salts of the mercaptotetrazoles may alsobe reacted with chlorocarbonic acid esters, with produces symmetricalcompounds of the type 1 directly.

The preparation of a few of these compounds is described in detailbelow.

COMPOUND 1 A solution of 11 g. of phosgene in 200 ml. oftetrachloromethane which has been freshly prepared at 5 C. isslowlyadded dropwise at 20 C. to a suspension of 40 g. (0.2 mol) of thesodium salt of 1-phenyl-5-mercaptotetrazole in 300 ml. of anhydroustetrachloromethane, whereby the tetrazole is dissolved and the sodiumchloride precipitates from this solution after some time. The reactionmixture is stirred for 4 to 5 hours at 50 C. and the solvent is thendistilled off. The oily residue is taken up in ether, filtered and thefiltrate is precipitated with petroleum ether. Compound 1 of m.p.l38-l39 C. is obtained after recrystallization from ether/petroleumether.

COMPOUND 6 17.8 g. of l-phenyl-5-mercaptotetrazole are dissolved in 50ml. of dry tetrahydrofuran and a solution of 15.35 g. (0.1 mol) ofp-chlorophenyl isocyanate in 50 ml. of tetrahydrofuran is addeddropwise. The solvent is concentrated by evaporation and the residue isprecipitated with ether/petroleum ether.

The chlorocarbonic acid thioester of l-phenyl-S-mercaptotetrazole, whichcan be prepared as described below, is used as an intermediate forcompounds 2, 3 and 8.

A vigorous stream of phosgene is passed into a suspension of 20 g. (0.1mol) of the sodium salt of l-phenyl-5-mercap totetrazole in 250 ml. ofdry tetrachloromethane, which causes a substantial amount of the salt todissolve. The reaction mixture is then left to stir for 2 hours, whilesodium chloride precipitates. This is removed by suction filtration. Themother liquor is slowly concentrated by evaporation, a syrupy residuebeing obtained which can be used directly. The chlorocarbonic acidthioester need not be isolated for the preparation of the compoundsdescribed below.

COMPOUND 2 The syrupy chlorocarbonic acid thioester is taken up in 200ml. of anhydrous tetrachloromethane, and 15.2 g. of the sodium salt ofl-ethyl-5-mercaptotetrazole are added. The reaction mixture is heated to60 C. with stirring for 2 hours, the solution is concentrated byevaporation, taken up in ethanol and filtered, and the product isprecipitated with petroleum ether. The resulting compound 2 isrecrystallized from ether/petroleum ether.

COMPOUND 3 The same procedure is employed as that used for compound 2,but 21.4 g. of the sodium salt of l-benzyl-S-mercaptotetrazole is used.

COMPOUND 4 The syrupy thioester is taken up in 200 ml. of anhydroustetrachloromethane, and 16.6 g. of the sodium salt of 1propyl-S-mercaptotetrazole are added. The reaction mixture is heated to60 C. with stirring for 2 hours and the resulting solution is filteredfrom the precipitated sodium chloride, concentrated by evaporation,taken up in ether and clarified with charcoal, and compound 4 isprecipitated by adding petroleum ether.

COMPOUND 5 COMPOUND 7 The procedure is analogous to that used forcompound 5 but 8.03 g. (0.11 mol) of n-butylamine are added instead ofmethylamine.

Compound 8 The procedure is analogous to that used for the preparationof compound 5 but 8.03 g. (0.11 mol.) of diethylamine are added.

The S-mercaptotetrazole derivatives which may be used according to theinvention can be hydrolysed relatively easily, especially in alkalinemedia. Apart from being added to the silver halide emulsion layers, theymay also be added to other layers since in any case they diffuse intothe silver halide em ulsion layers before or during development. Otherlayer to which the substance is added may be water permeableintermediate or protective layers.

Since the mercapto group is protected, the sensitivity obtainable in thephotographic emulsion is generally greater than when using stabilizerswith free SH groups. The sensitivity is not deleteriously effectedduring storage.

A further advantage of the inventive emulsion is that images ofparticular fine grains are obtained. This effect is caused by thehydrolysis of the compounds in the alkaline developer to produce freemercapto groups, and which gradually slows down the development. At thesame time, the maximum sensitivity is not reduced by the delayed releaseof the SH-group.

The tetrazole compounds can be added to the silver halide emulsion atany stage during the preparation of the emulsion.

It is preferred to incorporate these compounds before theafter-ripening.

The photographic silver halide emulsions are prepared in accordance withcommon practice including the steps of:

l. Precipitation of the silver halide in the presence ofa protectivecolloid and physical ripening;

2. Removal as by washing from the resulting emulsion, the excesswater-soluble salts that have formed as a result of the precipitation;and

3. Chemical ripening (after-ripening) the washed product to impart thedesired sensitivity to the emulsion.

The stabilizers according to the invention can be used in any silverhalide emulsion. Suitable silver halides for the emulsion are silverchloride, silver bromide or mixtures thereof, if desired containing upto 10 mols percent of silver iodide. The silver halides may be dispersedin the usual hydrophilic compounds such as carboxymethyl cellulose,polyvinyl alcohol, polyvinylpyrrolidone, alginic acid and its salts,esters or amides or, preferably, gelatin.

The methods of incorporating the stabilizers in emulsions are relativelysimple and well-known to those skilled in the art of emulsion making. Itis convenient to add the stabilizers from solutions in appropriatesolvents whereby the solven t kg. of emulsion. The specificconcentration depends on the The emulsion which is ready for casting isdivided into 4 type of the emulsion and on the effects desired. Theoptimum parts. concentration for any given emulsion will be apparent tothose Part A is used as a control without further additive; skilled inthe art upon making the tests and observations PartB contains anadditional 1 mg. ofstabilizer No. l; customarily employed in the art ofemulsion making. 5 Part C contains an additional 5 mg. of stabilizer No.l;

The emulsions can also be optically sensitized with cyanine Part Dcontains an additional mg. of stabilizer No. l. rhodacyanine ormerocyanine dyes such as described by F. M. The samples are applied ontoa cellulose acetate support, l-lamer The Cyanine Dyes and relatedCompounds lnterexposed in a sensitometer behind a grey step wedge, andscience Publishers, (1964). developed at 20 C. in a developer of thefollowing composi- The emulsions may also contain chemical sensitizers,e.g. 1 tion: reducing agents such as stannous salts, polyamines such assodium sulfite anhydrous 7.0 g. diethyltriamine or sulfur compounds asdescribed in U.S. Pat. borax 7.0 g. No. 1,574,944. For chemicalsensitization, one may further hydroquinone 3.5 g. add to the givenemulsions salts of noble metals such as p-monomethylaminophenol 3.5 g.ruthenium, rhodium, palladium, iridium, platinum or gold, as sodiumcitrate 7.0 g. described in the article by R. Koslowsky, Z. Wiss. phot.46, P ium mi 3- 65-72 (1959). The emulsions may also containpolyalkylene m P to 1 With Walerv oxides, especially polyethylene oxide,and derivatives thereof, The res lt o the sens ometr c tests are givenin table I as chemical sensitizers. below.

TABLE 1 Ai'telrI 3 days bstorgge in eat cup oar Development time 6Development time 16 Development time 16' Sensitivity SensitivitySensitivity in DIN 'y Fog in DIN 1 Fog in DIN Fog Control 0. 44 0.11Control 0.86 0.12 =1=0 0.80 0.15 +0.5 0.41 0.08 i0 0.88 0912 +0. 5 0. 840.13 3:0 0.42 0.07 :bO 0.79 0.11 +1 0.81 0.12 :i:0 0.39 0.06 0.5 0.780.09 .5 0.80 0.09

The emulsions according to the invention may additionally Thefog-stabilizing effect can be clearly seen both after 6 contain theusual stabilizers, e.g. homopolar or salt-type comminutes and after 16minutes development time, without the pounds of mercury with aromatic orheterocyclic rings, such sensitivity being reduced. The stabilizingeffect is maintained as mercaptotriazoles, simple mercury salts,sulfonium mercury even on storage in the heating cupboard. double salts,and other mercury compounds. Other stabilizers which may be used includeazaindenes, especially tetraalain- EXAMPLE 2 denes or pentaazamdenes, inparticular those substituted with Another Series of tests was designedto demonstrate that a hydrofyl ammo q l comPounds W have beenfog-stabilizing effect is obtained even without the use of an descnbedarticle photazaindolizine as a basic stabilizer although on comparisonwith (1952). Other suitable stabilizers include heterocyclic mertable 1the Synergistic ff obtained using the combination Capto f p q f- P l F Pquaternary with an azaindene stabilizer is clearly apparent.benzthlalole denvanves and benzufazoies' As is described in example 1, asimilar emulsion is prepared The emulsions y be hardened the usualmanner for for casting in the same manner but without the addition ofthe ample, with formaldehyde or halogen-substituted aldehydesazaindolizine. that contain a carboxyl p mucobromic acid, The emulsionwas divided into 3 parts with the following addiketones, methanesulfonicacid esters and dialdehydes. ditions; The stabilizers which we havedescribed may be used in p A n- 1 a l ith f nh dditi various kinds ofphotographic emulsions. In addition to being p B i 5 mg ofcompound N 1useful in X-ray and other nonoptically sensitized emulsions Th im n-i ls are shown i m 2 TABLE 2 After 3 days storage in heat cupboard;Development time 6 Development time 16 Development time 16 SensitivitySensitivity Sensitivity in DIN 'r Fog in DIN 7 Fog in DIN y Fog Sample.

A Control 0.52 0. 10 Control 0. 76 0.15 8.6 0.34 0.60 B 2 0.51 0.06 -20.73 0. 09 -2.5 0.69 0.30

NOTE: 3=1 shutter opening or double sensitivity.

they may also be used in orthochromatic, panchromatic and EXAMPLE 3infrared-sensitive emulsion. They may also be used for emulsionssuitable for use in the silver salt diffusion process for 5color-photographic emulsions and for photographic materials for thesilver dye bleach process.

The stabilizers provided by the invention can also be applied to greatadvantage during after-ripening, as will be seen from the followingexamples.

A silver iodobromide emulsion containing 8 mols percent of EXAMPLE 1silver iodide is prepared in the usual manner. For after-ripening, thepAg value is adjusted to 8.9 and the pH to 6.8 and the A highlysensitive silver iodobromide gelatin emulsion convi osity to about 20op. The emulsion is then treated with taining 8 mols percent of Agl isprepared for casting by adding gold-I-thiocyanate and divided into fourequal parts; (based 200 mg. of4-hydroxy-6-methyl-i,3,3a,7-tetraazaindene, 600 on 300 g. of AgBr, 8percent Agl).

mg. of saponin as wetting agent and 10 ml. of a 10 percent PartA controlsample without further additives;

aqueous formaldehyde solution as hardener per kg. of emul- Part Badditionally contains 8 mg. of compound 1;

sion. Part C additionally contains 10 mg. of compound 2;

Part D additionally contains 12 mg. of compound 3.

After-ripening is continued until maximum ripening has been obtained,and the samples are made ready for casting by the addition of 600 mg. ofsaponin as wetting agent, ml. of a 10 percent aqueous formaldehydesolution as hardener and 200 mg. of 4-hydroxy-6-methyl-l,3,3a,7-tetraazaindene as basic stabilizer, all per kg.

The samples are then cast on a cellulose acetate support, exposed in asensitometer behind a grey step wedge and developed at C. for 6 and I6minutes in the developer described in example 1.

The results of the sensitometric tests are shown in table 3.

TABLE 3 EXAMPLE 5 Another series of tests was designed to demonstratethat the compounds according to the invention have a considerably betterstabilizing effect than the known basic compound 1-phenyI-S-mercaptotetrazole. A highly sensitive silver iodobromideemulsion containing 5 mols percent of silver iodide was divided intofive equal parts. (Amount used based on 300 g. of silver bromide).

Part A control sample without additives; Part B contains 4 mg. ofcompound 1; Part C contains 6 mg. of compound 1;

After 3 days storage in heat cupboard;

Development time 6 Sensitivity Sensitivity Sensitivity in DIN 'y Fog inDIN y Fog in DIN 'y Fog Sample A Control 0.56 0.09 Control 0.85 0. 15+0. 5 0.82 0.37 B +0.5 0.51 0.08 +0.5 0.91 0.14 +0.3 0.81 0.28 C +0.50.50 0.07 +0.3 0. 90 0.12 +0.2 0 78 0.26 D +0.5 0. 49 0.07 1:0 2 0.880.13 +0.3 0 79 0.29

NOTE: 3=1 shutter opening or double sensitivity.

The table also gives results of a storagetest: The unexposed Part Dcontains 8 mg. of compound 1; samples were stored for 3 days at 60 C.This test shows that Part E contains 3 mg. ofl'-phenyl-5-mercaptotetrazole.

not only is the formation offog suppressed in the fresh film but alsoafter storage in a heating cupboard, which gives an indication of thestabilization effect on storage.

EXAMPLE 4 The same emulsion used in A and B in example 3 is opticallysensitized by addition of 40 mg. of the panchromatic sensitizer of theformula:

and 20 mg. of the orthochromatic sensitizer of the formula:

TABLE 4 The emulsions ripened to maximum sensitivity at a pAg of 8.9, apH of 6.9 and a viscosity of about 15 op. The solutions were preparedfor casting by the addition of 600 mg. of saponin as wetting agent, 10ml. of a 10 percent aqueous formaldehyde solution as hardener and 200mg. of 4-hydroxy-6- methyl-l,3,3a,7-tetraazaindene as basic stabilizerper kg. of emulsion. The samples are applied onto a cellulose acetatesupport, exposed in a sensitometer behind a grey step wedge. Developmentis performed for 6 minutes at 20 C. in the developer given in example 1.The results of the sensitometric tests are shown in table 5 below.

TABLE 5 After 3 days storage in heating cupboard (60 C.)

Sensitivity Sensitivity in DIN 'y Fog in DIN 7 Fog Control 0.87 0. l2 0.2 0. 74 0. 18 :i:0 0.83 0. 08 :bO. 1 0. 75 0. l0 :l:0 0. 84 0. 07 +0. 20. 74 0. 10 :i:0 0. 82 0. 07 +0. 3 0. 73 0. 09 :l:0 0. 0. 12 +0. 2 0. 750. 16

NOTE: 3=1 shutter opening or double sensitivity.

At a given sensitivity, the stabilizing effect of the l-phenyl-S-mercaptotetrazole derivative according to the invention is better thanthe known 1-phenyl-mercaptotetrazole when used as a ripening additive.This not only reduces fogging in test samples of the freshly preparedfilm but also on samples which have been heated in a heating cupboard.Also, it takes twice as long to achieve complete ripening whenunsubstituted l-phenyl-mercaptotetrazoles are used.

We claim:

1. A light-sensitive photographic composition having at least one silverhalide emulsion layer, which contains a stabilizer ofthe followingFormula:

NN it 1%- After 3 days storage in heat cupboard;

Development time 6 Development time 16' Sensitivity SensitivitySensitivity Development time 16' in DIN 1 Fog in DIN 'y Fog in DIN 'yFog Control 0. 75 0. 18 Control 0. 0. 29 -O. 7 0. 84 0. 35 5:0 0. 81 0.12 0. 5 1. 05 0. 22 -0. 5 0. 80 0. 25

in which R is alkyl having up to three carbon atoms; phenyl or benzyl;Yrepresents l the grouping which is linked to the carbonyl group throughan oxygen or sulfur atom or (2) the group--NRR wherein R stands foralkyl or for a radical of the phenyl series, and R stands for 3. Thecomposition of claim 3, wherein the stabilizer is a symmetricalbis-tetrazole dithiocarbonic acid ester.

4. The composition of claim 4, containing the stabilizer of thefollowing formula:

5. The composition of claim 1, which contains in addition a stabilizerof the tetraazaindene series.

* t t i I

2. The composition of claim 1, wherein Y represents
 3. The compositionof claim 3, wherein the stabilizer is a symmetrical bis-tetrazoledithiocarbonic acid ester.
 4. The composition of claim 4, containing thestabilizer of the following formula:
 5. The composition of claim 1,which contains in addition a stabilizer of the tetra-azaindene series.